/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.jhlabs.scany.util;

import java.util.ArrayList;
import java.util.EmptyStackException;

/**
 * An implementation of the {@link java.util.Stack} API that is based on an
 * <code>ArrayList</code> instead of a <code>Vector</code>, so it is not
 * synchronized to protect against multi-threaded access.  The implementation
 * is therefore operates faster in environments where you do not need to
 * worry about multiple thread contention.
 * <p>
 * The removal order of an <code>ArrayStack</code> is based on insertion 
 * order: The most recently added element is removed first.  The iteration
 * order is <i>not</i> the same as the removal order.  The iterator returns
 * elements from the bottom up, whereas the {@link #remove()} method removes
 * them from the top down.
 * <p>
 * Unlike <code>Stack</code>, <code>ArrayStack</code> accepts null entries.
 * <p>
 * <strong>Note:</strong> this class should be bytecode-identical to the 
 * version in commons collections. This is required to allow backwards 
 * compability with both previous versions of BeanUtils and also allow 
 * coexistance with both collections 2.1 and 3.0.
 *
 * @see java.util.Stack
 * @since Commons Collections 1.0
 * @version $Revision: 555824 $ $Date: 2007-07-13 01:27:15 +0100 (Fri, 13 Jul 2007) $
 * 
 * @author Craig R. McClanahan
 * @author Paul Jack
 * @author Stephen Colebourne
 */
public class ArrayStack extends ArrayList<Object> {

	/** Ensure serialization compatibility */
	static final long serialVersionUID = 4952513157310856314L;

	/**
	 * Constructs a new empty <code>ArrayStack</code>. The initial size
	 * is controlled by <code>ArrayList</code> and is currently 10.
	 */
	public ArrayStack() {
		super();
	}

	/**
	 * Constructs a new empty <code>ArrayStack</code> with an initial size.
	 * 
	 * @param initialSize  the initial size to use
	 * @throws IllegalArgumentException  if the specified initial size
	 *  is negative
	 */
	public ArrayStack(int initialSize) {
		super(initialSize);
	}

	/**
	 * Return <code>true</code> if this stack is currently empty.
	 * <p>
	 * This method exists for compatibility with <code>java.util.Stack</code>.
	 * New users of this class should use <code>isEmpty</code> instead.
	 * 
	 * @return true if the stack is currently empty
	 */
	public boolean empty() {
		return isEmpty();
	}

	/**
	 * Returns the top item off of this stack without removing it.
	 *
	 * @return the top item on the stack
	 * @throws EmptyStackException  if the stack is empty
	 */
	public Object peek() throws EmptyStackException {
		int n = size();

		if(n <= 0) {
			throw new EmptyStackException();
		}

		return get(n - 1);
	}

	/**
	 * Returns the n'th item down (zero-relative) from the top of this
	 * stack without removing it.
	 *
	 * @param n  the number of items down to go
	 * @return the n'th item on the stack, zero relative
	 * @throws EmptyStackException  if there are not enough items on the
	 *  stack to satisfy this request
	 */
	public Object peek(int n) throws EmptyStackException {
		int m = (size() - n) - 1;

		if(m < 0) {
			throw new EmptyStackException();
		}

		return get(m);
	}

	/**
	 * Pops the top item off of this stack and return it.
	 *
	 * @return the top item on the stack
	 * @throws EmptyStackException  if the stack is empty
	 */
	public Object pop() throws EmptyStackException {
		int n = size();

		if(n <= 0) {
			throw new EmptyStackException();
		}

		return remove(n - 1);
	}

	/**
	 * Pushes a new item onto the top of this stack. The pushed item is also
	 * returned. This is equivalent to calling <code>add</code>.
	 *
	 * @param item  the item to be added
	 * @return the item just pushed
	 */
	public Object push(Object item) {
		add(item);
		return item;
	}

	/**
	 * Returns the one-based position of the distance from the top that the
	 * specified object exists on this stack, where the top-most element is
	 * considered to be at distance <code>1</code>.  If the object is not
	 * present on the stack, return <code>-1</code> instead.  The
	 * <code>equals()</code> method is used to compare to the items
	 * in this stack.
	 *
	 * @param object  the object to be searched for
	 * @return the 1-based depth into the stack of the object, or -1 if not found
	 */
	public int search(Object object) {
		int i = size() - 1; // Current index
		int n = 1; // Current distance

		while(i >= 0) {
			Object current = get(i);

			if((object == null && current == null) || (object != null && object.equals(current))) {
				return n;
			}

			i--;
			n++;
		}

		return -1;
	}
}
